Process of separating fragmentary materials



' Feb. 13, 1940- v. RAKowsKY E-r A1.

y PROCESS OF SEPARATING FRAGMENTARY MATERIALS Filed Feb. 15, 1938 N mZmXO-IP m4 v W Patented Feb. 13, 1940 UNITED ,STAT-Es PATENT OFFICE PROCESS OF SEPARATING FRAGMENTARY MATERIALS Victor Rakowsky, Joplin, Mo., and Ray W. Arms,

Chicago, Ill., assignors to Minerals Beneficiation Incorporated, Chicago, Ill., a corporation of Delaware Application February 15, 1938, Serial No. 190,670

3 Claims.

' ticles of various ores or other substances subjected to treatment.

It has been proposed heretofore to provide a liquid separating medium of increasing specic gravity from the top downward by introducing into a body of water a plurality of finely divided solids of differing specific gravities, the propor tions of water and the different solids being such as to provide a liquid medium in which the lighter particles to be separated will rise and 0 the heavier particles will sink therein. At the o great diiiiculty has been experienced in maintaining the required specific gravity of the medium. Among these causes may be noted'the following: lighter medium is removed from the top of the main body ofthe medium together vwith the lighter separated material and heavy medium is removed from the bottom together with the heavier separated material. Moreover, ythe materials to be separated are generally fed into the main body of the medium in a wet condition and even though they have been preavashed, they are frequently accompanied by slimes and other ne bodies of solids and water. i One of the objects of the present invention is to provide a method of separating fragmentary materials of different specific gravities in a sepyarating medium while maintaining in such medium at all times'specifc gravities required for accurate separation of the materials. Further o objects will appear as the description of4 the invention proceeds.

In the practice of thepresent invention a suitable self-supporting or self-sustaining medium is placed in a container or tank preferably of inverted cone shape, the specic gravity of the medium at the top of the tank being less than that of the material to be separated out, the specific gravity decreasing from the bottom upward.

This medium-is formed by mixing in water a finely divided heavy solid or solids of a specilc gravity not less than 7.0, such as galena or galena concentrates or nely divided metals. either alone or in association with a metallic mineral such as magnetite, in proper proportions with natural slimes (which sometimes contain magnetite) of the ores or other materials to be separated. These natural slimes may be and' -generally are accompanied .by other nely divided solids of high or low specific gravity.

Specific gravity.-In a solid plus water mixture, there is a denite mathematical relation between the average sp. gr. of the solids, the percentage of the solids, and the resulting sp. gr. ofthe suspension, expressed by the following formula:

d=specic gravity of pulp S =specific gravity of dry solids P= percent solids Thus in a galena plus slimes mixture having an average sp. gr. -of 5.9 it will require 72.2% of the solids to produce a medium of 2.50 sp. gr. at the top. This mathematical relationship is independent of the grain size of the solids.

Grain size- The self-supporting powers of a suspension medium are related tothe size of solid grains in said medium. The finer 'the grains, the greater is the self-supporting power.

However, iiuidity is increased by coarser grains. Therefore,v the ideal self-supporting medium is one in which there is a maximum amount of grains of a size contributing to self-support, and a maximum percentage of coarse grains for liquidity. In a medium of 2.5 top sp. gr., the maximum grain size of galeria which can be supported, is approximately 150 mesh. In a medium of a higher top speciflc gravity, larger galeria grains may be supported. It has been found that 2.80 top sp. gr., 100 mesh grains will not settle out, under operation conditions with a minimum of agitation. y

Most common non-metallic slimes such as clay and calcite, exhibit a greater tendency to A form'ne slimes than does galeria. They are also lighter and more buoyant. Galena is heavy, breaksv into granular particles, and in a pure state must be ground very fine to form, a selfsupporting medium.

We have discovered that by separating out a portion of the ne non-metallic slimes of a given ore to provide the supporting qualities, and adding thereto a proper. amount of the relatively coarser grains of ground galeria, for example,

to supply liquidity, an ideal medium is the resuit.

On account'pf the low cost of the natural slimes in the ore, it is obvious that the most economical medium will be one in which there is a maximum of such slimes. More of `such natural slimes may be used when the sp. gr. of the separation is low than when it is high. The measure of this mixture is usually made in terms` of metal in the mixture. Thus,k when galena is used it is in terms of lead in the mixture. Pure galenais 86.6% lead. At 2.50 top sp. gr. of medium it is possible to use solids of 55% lead and get good results.

Itis essential in the present invention that the heavier solid or solids of' the medium have a vspeciiic gravity of not less than'7.0. In the majority of the ores treated by a process of this character, the'sp. gr. of the gangue minerals to be separated out have a specilc gravity of at least 2.5, and in order that such gangue minerals may be caused to rise in the separating medium, it is essential that the medium at its upper portion should have a specic gravity of not less than 2.5. The use of the heavier solid of a sp. gr. of not less than 7.0 is essential to provide a medium having a top sp. gr. of 2.5 if the proper liquidity of such medium is to be preserved. It is also essential in the practice of the present invention that J`e separating medium be one which when bro-..ght to rest will remain liquid throughout its' entire depth for several hours, with the speciiic gravity thereof increasing from the top downward, and such a medium is herein referred to as a self-supporting or self-sustaining medium. Wi-"e the solids in such a vselfs'upporting medium may tend to very slowly settle when the liquid is" at rest, the settlement is in the nature of a movement of the solids 'is not entirely understood. It is probably the same force or combination of forces found in colloidal solutions. This may include an electrical force of attraction or repulsion. Whatever the force may be, the effects thereof are uniform and are of importance in the self-supported or selfsustaining medium of the present invention.

'While after several days settling of such a medium, the lower layers of the medium may be too thick to have any value as a separating medium, nevertheless if apparatus employed in the practice of the process is shut down for a few minutes, a few hours or even a day, said selfsustaining medium can readily be set in motion again by liquid handling means, such as stirring devices, pumps, air lifts and the like, and the medium than be restored to proper condition.

'Thus it will be apparent that one of the advantages of such a self-supporting medium is that there isvno clogging of tanks, pipes, pumps or accessories during normal shut-down periods, such as would be caused by solidified non-liquid layers of the settled particles of the medium.

Moreover, when in operation, the gentlest of stirring will resist settlement and preserve the proper iiuidic conditions indefinitely' with a'high differential between the top and bottom sp. gr. of the medium, and the stirring may be utilized to aid in maintaining the required differential between the top and bottom of the medium. 5

When ores to be separated are fed into a separating medium they are accompanied by a variety of slimes some of which have no metallic values, and some of which have more or less. metallic value, and in addition to this certain slimes are yl0 produced by the degrading action of the ore itself during the process. These slimes produced by the degrading action of the ore during the process may be of either o1 the two classes mentioned above.' If all of these slimes were perl5 mitted to remain in the medium during the process the result would be an accumulation of such slimes which would eventually soincrease the percentagethereof as to destroy the required specific gravity and liquidity of the self-sus- 20 taining medium.

Having determined the proper composition of the self-sustaining medium by test, experiment or otherwise, for the ore under treatment, it is of imperative importance that this composition 25 be maintained approximately constant. It will be recognized from the above that the composition of theself-sustaining medium is determined by the proportions of slimes of differing grain size and specific gravity and of the .water em- 30 ployed.

By the present invention steps are taken to withdraw from some point in the system an amount of medium for purification sucient so that the amount of slimes removed from such medium equals that developed in the system and supplied by the fragmentary materials fed to the process. By this means the composition of the medium is maintained approximately constant.

In such purification it is preferred to remove only 'i04 the required sp. gr. of said main body of selfsustaining medium. In some cases, however, it may be of advantage to also remove some of the slimes of metallic value. The advantage of re- 50 moving as little of the metallic slimes as possible resides in the fact that the metallic slimes are conserved and by their use the amount of high grade 7.0 sp. gr. material required in the medium is considerably reduced.

Having prepared a self-sustaining medium ofr the proper sp. gr. for the materials to be separated and the sp. gr. at or immediately below the surface being not less than 2.5, said materials are fed into the top of the medium with slimes 60 and other nely divided substances, as well as some water, and the lighter portions of the materialsto be separated rise in the medium and are removed therefrom together with a considerable` portion ofthe lighter part of the medium itself. 65 This top medium thus removed has a high percentage of slimes and their removal tends to materially lower the proportion of slimes remaining in the body of medium in the tank, while the incoming feed` of materials adds water and 70 slimes thereto. The heavier portions of the materials to be separated sink to near the bottom of the medium and are removed therefrom with a considerable amount of the heavier medium itself thus tending to reduce the' amount of such 75' heavy medium in the main body of medium. All this tends to change the sp. gr. of the medium remaining in the tank, and if the operation were thus continued efficient and accurate separation of the materials would soon become impossible. By' the present invention steps are taken to neutralise this tendency and'maintain the specific gravity of the body of medium in the tank at the proper pointfor accurate separation of the materials.

Let it be assumed that the fragmentary mate` rials to be separated require a specific gravity at the top of the separating medium of 2.5 or' higher, say 2.80, with the sp. gr. increasing downward until it is, say 2.96. When the fragmentary solids to be separated are fed linto this medium, they are accompanied by slimes vand other finely divided substances as well as water, and the lighter separated solids leaving the top ofthe tank are accompanied by water, slimes and other finely divided substances. Moreover, the heavier separated materials removed' from the bottom of the tank are accompanied by some of the heavier medium. As above stated, all this tends to produce a change in the specific gravity and liquidity of the medium remaining in the tank, and this change tends to defeat 'efficient and accurate separation of the fragmentary materials under treatment. The extent of this change is determined by test experience or otherwise and will vary with different ores., with the rate of feed of said ores to the tank and for other reasons.

In the operation of -our process there is developed a certain amount of slimes both in the o're feed and due to the degrading action of the ore itself during the process. This results in an accumulation of slime from the ore itself winch would eventually increase the percentage of slime above that desired in the system if steps were not taken to avoidit.' In our invention steps are taken to withdraw from some point in the system an amount of medium for purification sumcient so that the amount of slimermoved from such medium is approximately the same asthat developed in the system and supplied by the fragmentary materials fed to the process. This medium more or less cleaned or purified is continuously returned to the main' body of medium in the tank in such amount andat such a rate as to constantly maintain the required sp. gr'. and liquidity of the medium in the tank.

The preferred method of doing this will be understood by reference to the accompanying dia? gram in which l indicates any suitable separating tank, and 2 an ore feeding chute. The lighter separated material with accompanying medium overflows at 3 onto screen 4 and the medium passes through the screen into tank 5, while the separated materials with some of the solids of the medium clinging thereto pass down the screen 4 and over the tank 6 where they are sprayed with water, thus washing off the clinging solids, and the wash water and solids thus washed off pass through the screen and into tank 6. The heavier separated materials with accompanying medium are elevated tlucugh pipe 'l by an air lift device 8 and are delivered at 9 onto a screen 4. The medium passes through the screen 4 onto a chute or pan I which delivers the main portion ...hereof into the separating tank. The separated materials falling upon the screen 4 pass down the screen over the tank I3, and While over said tank they are sprayed with water to wash off any of the solids of the medium which may be clinging thereto, the washed water and solids thus washed of! passing through the screen into the tank I3. From the tank 5 the medium therein isreturned as indicated by the arrow to the top of the medium in the tank, preferably by way of the feed chute 2. It will thus be seen that by far the larger portion of the medium removed from the tank either from the top or from the bottom is returned directly to the medium in the tank. In ordinary practice this exceeds 90% of the medium thus removed, and provision is made for treating that portion of the medium which is not thus directly returned so as to clean or purify it by removing some of the natural slimes and de-` naturalslimesand degraded slimes from the medium. For the purpose of removing these slimes and sands from the wash water in tanks 6 and I3, the wash water with associated slinies is conducted to any suitable cleaning means A', wherein any desired portion of the slimes and sands are removed, and the water with the remaining portions pass therefrom directly into the thickener tank I4. From the slotted pipe or trough l2 the portion of medium received therein is preferably first conducted to any suitable cleaning means A3, wherein any desired portion of the 'slimes and sands is eliminated, the medium thus cleaned passing into the thickener tank' I4. If desired, however, the cleaning means A3 may be omitted and the medium passed directly from the slotted pipe or trough I2 to the thickener tank I4. Likewise, the medium from the tank 5 may be treated in the cleaning means A3. =The medium thus vtreated is passed from the cleaning means A3 directly to the thickener tank I4. If

found necessary, the medium in the thickener tank I4 may be passed through a cleaning means A2 and back from said means to the thickener itself as indicated in dotted lines. The cleaning means A', A2 and A3 thus provide means whereby the medium in the tank I4 may have any desired portion of the slimes and sands therein removed, and this proportion removed is so regulated that when the medium from the thickener I4 is passed therefrom by way of the conduit I5 back to the tank I they will be in such a condition as to sp. gr. and liquidity that they will serve to neutralize or overcome the tendency to the` change of sp. gr. and liquidity due to incoming water and slimes in the tank mentioned above, thus maintaining in thei'tank a medium of constant composition. This return of the medium from the tank 5 and by way of the chute I0 and from the thickener I4 to the tank I is continuous, that from the thickener I4 being regulated in amount and rate to maintain constant the composition of the medium in the tank. The amount thus returned and the rate of return will vary with different ores, as well as with the rate of feed of the ore, and the operator determines by test and experience what the amount and rate of return is required in each particular -case to maintain the composition of the medium in the separating tank constant.

It will be noted that the medium in the tank 5 is the top medium from the separating tank, and that the portion of the medium in the tank 5 that passes to the cleaner A3 is an overow from the tank 5 to said cleaner. The result of this is that the medium that passes to the cleaner A3 is the medium that contains not only the slimes of the ore being treated but also the finer particles of the solid, such as galena, contained in said medium; and it is these exclusively iine particles of both kinds that unless removed before the medium is returned to the separating tank, would tend to materially change the proportions of grain size in the medium, thereby changing its composition and specific gravity and destructively increasing the viscosity and decreasing the liquidity of the medium in the separating tank. It is in order to avoid this deleterious change in the composition of the medium in the tank that slimes are removed from some of the medium before it is returned to the tank.

It will thusl be seen that those constituents entering into thecomposition of the mediumwhich would tend to produce undesirable viscosity of the medium are removed to such an extent as operating conditions may require in order to maintain the composition of the medium constant, i. e., approximately that of the medium at the initiation of the operation.`

By these steps the heavier solids (such as galena or metals) in the medium, as well as the valuable portion of the natural slimes are conserved in the thickener, onlyvalueless portions of 'the natural slimes and sands being discarded by way of the cleaning means A', A2 and A3.

While for the purpose of description, more particular reference has been made herein to galena (and metals) is is to be expressly understood that the invention is not limited to the use of galena as the heavy solid in the medium. It has been demonstrated that iron (by which term as herein used steel is included) in powdered form, either alone or with magnetite or other magnetic minerals are of high eiiiciency when substituted for galena in the detailed description heretofore given. i l

One of the outstanding advantages resulting from the use of iron, either alone or with magnetite, or other magnetic minerals lies in the fact that they are readily recovered from the medium by well-known magnetic means. The heavier solids (galena, metals, etc.) of not less than 7.0 sp. gr. designed to be employed in the process are much more expensive than clays, sands and the like Which have heretofore been employed in the art, and it is, therefore essential from an economical standpoint that these heavier solids be recovered for re-use without waste. When this is accomplished the initial cost of the heavier solid in the medium is practically the entire cost of such medium. Furthermore, by adding to the galenaI metallic slimes other than galena, such as natural slimes of the metallic minerals being treated or those produced by degradation, there is an appreciable saving in the capital cost of the ,mediumvitseli It will be further appreciated that by using minerals or metals having a specic gravity of 7.0, the quantity of such minerals or metals required in the medium when mixed with the natura'l slimes of the ore and those produced by degradation is below that which would be required if minerals or metals of a lower specificgravity were employed and. thus the capital cost of the medium is appreciablyreduced.

An additional advantage lies in the fact that minerals or metallics having a specic gravity of 7.0 are readily recovered at a low cost by well known cleaning processes. Galena, for example, is easily and cheaply recovered by flotation processes; and, because of its specific gravity, by tabling or classication. Steel and magnetlte are easily and cheaply cleaned or puriiied by magnetic concentration means or other means. The conservation of water is also of importance particularly in localities where water' is scarce, and in the closed circuit of the process herein described the water is used over and over in the washing of the medium remaining attached to the removed rock, and hence a minimum amount of water is required.

It is to be particularly pointed out that by the use of metals such as steel, iron, copper, zinc, etc., having a specific gravity of 7.0 or higher, as the'heavy solid in the medium, it is rendered possible in treating any particular ore to avoid contamination of the values recovered from the ore resulting from the use of the medium. For example, in treating iron ore, steel or iron or its alloys may be employed as the heavy solid in the medium rather than galena, since steel or iron would not contaminate the recovered values, Whereas the lead in galena would. The same is true if copper were used as a solid in the medium for treating copper ores or zinc were used as a solid in treating zinc ores.

What is claimed is:

l. In a process of separating ores the use of a liquid self-supporting separating medium comprising .Water containing slimes of the ore to be separated together with a comminuted solid of not less than 7. specic gravity, the slimes and comminuted solids being in such proportion that the mixture of slimes and comminuted solid shall have a specific gravity of not less than 5.9, the said slimes and comminuted solid constituting in excess of .70%, 'by weight, of the separating medium.

2. In a process of separating ores the use of l a liquid self-supporting separating medium comprising water containing slimes of the ore to be, separated together with granulated galena, said slimes and galena being in such proportions that the mixture of slimes and galena shall have a specific gravity not less than 5.9, and the slimes and galena constituting not less than by Weight, of the separating medium.

3. In a process of separating ores, the use of a self-supporting separating medium comprising Water and a nely granulated solid of a specific gravity of not less than 7. suspended in the water by natural slimes of the ore being treated, the slimes and granulated solid being in such proportions that` the specic gravity of the mixture of the two is not less than 5.9, and the saidslimes and granulated solid constituting in excess Aof 70% by weight, of the separating medium.

VICTOR RAKOWSKY,

RAY W. ARMS. 

